Direct integration of feedthrough to implantable medical device housing with ultrasonic welding

ABSTRACT

One aspect is an implantable medical device including a metal housing configured for implantation in a human and including a biocompatible metal and defining an opening. A feedthrough device is configured within the opening of the metal housing and includes an insulating section and a conducting section, the insulating section electrically isolating the conducting section from the metal housing. An ultrasonic joint is configured between the feedthrough device and metal housing that hermetically and mechanically bonds the feedthrough device and metal housing. The biocompatible metal of the housing is a microstructure primarily having α-phase grains.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/104,644, entitled “DIRECT INTEGRATION OF FEEDTHROUGH TO IMPLANTABLEMEDICAL DEVICE HOUSING WITH ULTRASONIC WELDING,” having a filing date ofDec. 12, 2013, which is incorporated herein by reference.

This Patent Application is related to Ser. No. 14/104,636, filed Dec.12, 2013, entitled “DIRECT INTEGRATION OF FEEDTHROUGH TO IMPLANTABLEMEDICAL DEVICE HOUSING USING A GOLD ALLOY” having Attorney Docket No.H683.138.101/P12045 US and Ser. No. 14/104,653, filed Dec. 12, 2013,entitled “DIRECT INTEGRATION OF FEEDTHROUGH TO IMPLANTABLE MEDICALDEVICE HOUSING BY SINTERING” having Attorney Docket No.H683.141.101/P12148 US, all of which are incorporated herein byreference.

BACKGROUND

Implantable medical devices, such as cardiac pacemakers, cardiacdefibrillators, and neurostimulators, receive and/or deliver electricalsignals to/from portions of the body via sensing and/or stimulatingleads. Implantable medical devices typically include a metal housing(typically titanium) having a hermetically sealed interior space whichisolates the internal circuitry, connections, power sources, and otherdevice components from body fluids. A feedthrough device (often referredto simply as a feedthrough) establishes electrical connections betweenthe hermetically sealed interior space and the exterior bodily fluidside of the device.

Feedthroughs typically include an insulator (typically ceramic) andelectrical conductors or feedthrough pins which extend through theinsulator to provide electrical pathways between the exterior and thehermetically sealed interior. A frame-like metal ferrule is disposedabout a perimeter surface of the insulator, with the ferrule andinsulator typically being joined to one another via a brazing orsoldering process. The ferrule is configured to fit into a correspondingopening in the metal housing, with the ferrule being mechanically andhermetically attached to the housing, typically via laser welding. Theinsulator electrically insulates the feedthrough pins from one anotherand from the metal ferrule/housing.

The ferrule is typically joined to insulator via a welding or brazingprocess. However, the high temperatures employed by such processes heatsthe titanium of the housing about the perimeter of the opening to levelsthat cause a structural change in the titanium, commonly referred to as“grain growth”. This structural change can distort the dimensions of theopening and cause the titanium about the perimeter of the opening tobecome less rigid, each of which can result in a weaker joint betweenthe ferrule and the housing.

Additionally, machining the ferrule (typically from pure titanium) toprovide a high tolerance gap between the ferrule and the insulator(about 10-50 μm) which is necessary to achieve a quality braze joint isdemanding and costly. Furthermore, if the gap is not maintained duringthe brazing process, or if the brazing process itself is not properlyperformed, a weak joint may be formed that can lead to premature failureof the implantable device.

For these and other reasons there is a need for the embodiments of thepresent disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of embodiments and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments andtogether with the description serve to explain principles ofembodiments. Other embodiments and many of the intended advantages ofembodiments will be readily appreciated as they become better understoodby reference to the following detailed description. The elements of thedrawings are not necessarily to scale relative to each other. Likereference numerals designate corresponding similar parts.

FIG. 1 generally illustrates an example of an implantable medical deviceaccording to one embodiment.

FIGS. 2 illustrates a feedthrough device in an implantable in accordancewith the prior art.

FIG. 3 illustrates a cross-sectional view of a feedthrough in animplantable medical device in accordance with one embodiment.

FIG. 4 illustrates a system for fabricating a feedthrough assembly in animplantable medical device in accordance with one embodiment.

FIG. 5 illustrates a system for fabricating a feedthrough assembly in animplantable medical device in accordance with one embodiment.

FIG. 6 illustrates a method for fabricating a feedthrough assembly in animplantable medical device in accordance with one embodiment.

DETAILED DESCRIPTION

In the following Detailed Description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments in which the invention maybe practiced. In this regard, directional terminology, such as “top,”“bottom,” “front,” “back,” “leading,” “trailing,” etc., is used withreference to the orientation of the Figure(s) being described. Becausecomponents of embodiments can be positioned in a number of differentorientations, the directional terminology is used for purposes ofillustration and is in no way limiting. It is to be understood thatother embodiments may be utilized and structural or logical changes maybe made without departing from the scope of the present invention. Thefollowing detailed description, therefore, is not to be taken in alimiting sense, and the scope of the present invention is defined by theappended claims.

It is to be understood that the features of the various exemplaryembodiments described herein may be combined with each other, unlessspecifically noted otherwise.

One embodiment is a method of securing a feedthrough to a metal housingfor an implantable medical device. The method provides the feedthroughincluding an insulating section and at least one conductive sectionextending through the insulating section. At least a portion of theinsulating section is metalized. The metalized feedthrough is placedwithin an opening in the metal housing of the implantable medicaldevice. The feedthrough and metal housing are positioned within anultrasonic welding system. The ultrasonic welding system is energizedsuch that ultrasonic energy welds the feedthrough directly to the metalhousing. The temperature of the metal housing is not raised above theβ-transus temperature of the metal housing during the ultrasonicwelding.

Accordingly, significant heat is avoided in securing the feedthroughdirectly to the metal housing thereby avoiding structural changes in themetal housing. Where the housing is a metal, such as titanium, avoidingsignificant heating levels prevents grain growth in the titanium, whichcan cause undesirable dimensional changes, cause perimeter areas ofopenings to become less rigid and lead to a weakened or defective joint.

In one embodiment, the method includes positioning the feedthrough andmetal housing within the ultrasonic welding system and furtherpositioning the feedthrough and metal housing between a first portionand a second portion of the ultrasonic welding system and such that thefirst portion contacts only the feedthrough on a first side and thesecond portion contacts only the metal housing on a second side oppositethe first side as the first and second portions of the ultrasonicwelding system are forced together.

Forcing the feedthrough on one side against the metal housing with aforce the opposite side creates a force at the interface between thefeedthrough and housing thereby facilitating a high-quality ultrasonicjoint between them.

In one embodiment, the method further includes placing a bond materialbetween the metalized feedthrough and the metal housing such that thetemperature of the metal housing, the metalized feedthrough, and thebonding material is not raised above the β-transus temperature of themetal housing and the metalized feedthrough during the ultrasonicwelding. Avoiding high temperatures while securing the feedthroughdirectly to the metal housing, also avoids structural changes in themetal housing and leads to a superior joint.

In one embodiment, the method is used wherein the temperature of themetal housing is kept below 890° C. while the ultrasonic welding systemis energized and the feedthrough is welded to the metal housing, and inanother, the temperature of the metal housing is kept below 750° C.Again, avoiding high temperatures avoids structural changes in the metalhousing and leads to a superior joint.

In one embodiment, the method is used wherein the temperature of themetal housing is controlled while the ultrasonic welding system isenergized and the feedthrough is welded to the metal housing such thatthe metal housing does not experience significant grain growth. Inanother, the temperature is controlled such that the microstructure ofthe metal housing remains primarily α-phase grains having an averagegrain size of less than 425 μm and in another embodiment, such that themicrostructure of the metal housing remains primarily α-phase grainshaving an average grain size in the range of 10-40 μm. Avoidingsignificant heat levels while securing the feedthrough directly to themetal housing, avoids structural changes in the metal housing and leadsto a superior ultrasonic joint between the feedthrough and metalhousing.

In one embodiment, an implantable medical device includes a metalhousing configured for implantation in a human and a biocompatible metaland defining an opening. A feedthrough device is configured within theopening of the metal housing and includes an insulating section and aconducting section, the insulating section electrically isolating theconducting section from the metal housing. An ultrasonic joint is madebetween the feedthrough device and metal housing that hermetically andmechanically bonds the feedthrough device and metal housing. Thebiocompatible metal of the housing has a microstructure primarily havingα-phase grains.

Accordingly, since the biocompatible metal of the housing is primarilyα-phase grains that are smaller grains and, thus, more grain boundaries,are harder than metals having larger grains, which have fewer grainboundaries. As a result, the primarily α-phase smaller grains are aclose-packed hexagonal crystal structure, which allows for lessdimensional changes thereby leading to a superior ultrasonic jointbetween the feedthrough device and metal housing.

In one embodiment, the implantable medical device is furthercharacterized in that the biocompatible metal of the housing comprises amicrostructure having substantially no β-phase grains. Because β-phasegrains are larger than α-phase, the β-phase grains can cause dimensionaldistortions in the metal housing. Avoiding this leads to a more rigidperimeter of the opening and a better seal being formed between thehousing and the feedthrough.

In one embodiment, the implantable medical device further includes abiocompatible bonding material between the feedthrough device and metalhousing to help create a strong ultrasonic joint therebetween. In oneembodiment, the implantable medical device has a metal housing oftitanium, niobium or a combination thereof.

In one embodiment, the implantable medical device has a metal housingwith a metal having an average grain size less than 300 μm, in one casean average grain size less than 100 μm, and in one case an average grainsize in the range of 10-40 μm. Because of the smaller grain sizes, thegrains are close-packed, which allows for less dimensional changes inthe housing, thereby leading to a superior ultrasonic joint between thefeedthrough device and metal housing.

In one embodiment, an interface between the feedthrough and metalhousing is substantially angled relative an exterior surface of themetal housing. The angled exterior surfaces facilitate forcing thefeedthrough against the metal housing causing a force at the interfacebetween the feedthrough and housing thereby facilitating a high-qualityultrasonic joint between them.

In one embodiment, the implantable medical device has a width on theopening of the housing that is smaller than a width of the feedthroughdevice at its widest distance between two opposing sides. The overlapcaused by the difference in width between the housing and thefeedthrough device facilitates the welding of a high-quality ultrasonicjoint between them.

In one embodiment, an implantable medical device includes a housinghaving an opening with an opening width. A feedthrough includes aninsulator having a bottom surface and side surfaces and having aninsulator width between opposing side surfaces that is greater than theopening width. An ultrasonic joint between at least one of the bottomsurface, top surface, and side surfaces of the insulator and the housinghermetically seals the insulator to the housing.

In one case, the overlap caused by the difference in width between thehousing and the feedthrough device facilitates the welding of ahigh-quality ultrasonic joint between them.

In one embodiment, the implantable medical device has an insulator widthbetween opposing side surfaces that is two times greater than theopening width. This allows sufficient space for the welding of ahigh-quality ultrasonic joint between them.

In one embodiment, the implantable medical device has a housing that isa biocompatible metal with a microstructure primarily having α-phasegrains, and in one case has a microstructure having substantially noβ-phase grains and in one case has an average grain size less than 300μm. Because of the smaller grain sizes, the grains are close-packed,which allows for less dimensional changes in the housing, therebyleading to a superior ultrasonic joint between the feedthrough deviceand metal housing.

FIG. 1 is a block and schematic diagram generally illustrating oneembodiment of an implantable medical device 30, such as a cardiacpacemaker for example. Implantable medical device 30 includes ahermetically sealed metal case or housing 32, typically formed oftitanium, which defines a hermetically sealed interior space 34 in whichdevice electronics 36 are disposed and protected from fluids of the bodyfluid side 38 external to housing 32. A header 40 attaches to housing 32and includes a connector block 42, which typically includes one or moresockets for connecting to one or more sensing and/or stimulating leads44 that extend between implantable medical device 30 and desired regionsof the body, such as the human heart and brain, for example. Afeedthrough device 50 establishes electrical pathways or connectionsthrough housing 32 that maintain the integrity of hermetically sealedinterior space 34 and provide electrical connection of leads 44 tointernal device electronics 36.

FIG. 2 is a cross-sectional view illustrating portions of an implantablemedical device, such as medical device 30 of FIG. 1, including metalhousing 32 having an opening 46 in which a conventional feedthroughdevice 50 is positioned. Feedthrough device 50 includes an insulator 52,feedthrough pins or conducting elements 54, and a ferrule 56. Ferrule 56is a frame-like metal structure that holds insulator 52 and which isconfigured to fit into opening 46 for attachment to housing 32. Ferrule56 is a bio-compatible material, typically titanium, which ismechanically and hermetically attached to housing 32 by laser welds 58,or similar techniques. Ferrule 56, as illustrated in FIG. 2, sometimesincludes a flange 60 to further aid in securing ferrule 56 to housing32.

Conducting elements 54 extend through openings or vias 62 in insulator52 and are formed of an electrically conductive material so as toprovide electrically conductive pathways from the external body fluidside 38 of housing 32 to hermetically sealed interior space 34.Insulator 52 is formed of a non-electrically conductive material, suchas a ceramic material, aluminum oxide (Al₂O₃) for example, andelectrically isolates conducting elements 54 from one another and fromferrule 56 and housing 32.

When attaching insulator 52 and ferrule 56 to one another, a perimetersurface of insulator 52 is typically metalized (through a sputtercoating process, for example) to provide a thin metal coating 64thereon. Ferrule 56 is then joined to insulator 52 via metal coating 64using a braze 66, such as of gold, for example, to form a biocompatibleand hermetic seal. Similarly, interior surface of vias 62 are providedwith a metal coating 68 and a braze 70 (e.g. gold) is used to coupleconducting elements 54 to insulator 52 and form a biocompatible andhermetic seal.

In order to achieve a quality braze, and thereby a quality hermeticseal, a proper gap must be maintained between ferrule 56 and insulator52 during the brazing process (typically about 10-50 um) so that thebrazing material (e.g. gold) is properly drawn into the gap by capillaryaction to create a strong and reliable braze 66. Forming ferrule 56,typically via machining processes, to meet the tight tolerances requiredto provide the proper gap with insulator 52 as well as to the dimensionsof opening 46 in housing 42 is time consuming and costly. Also, duringthe brazing process, intermetallics are formed between the brazingmaterial (e.g. gold) and the material (e.g. titanium) of ferrule 56,with the intermetallics being brittle as compared to the brazingmaterial. If the gap between ferrule 56 and insulator 52 is too small,the amount of intermetallics may be large relative to the amount of purebrazing material (e.g. gold) resulting in a brittle braze 66 that maycrack and comprise the hermitic seal.

Additionally, heat from the brazing (or welding) of ferrule 56 tohousing 32 can cause structural changes in the titanium of housing 32about opening 46 (and to ferrule 56) due to “grain growth” in thetitanium. Such “grain growth” can cause undesirable dimensional changesin opening 46 and can cause the titanium about the perimeter of opening46 to become less rigid (i.e. more flexible), which such changes leadingto a weakened or defective joint.

All polycrystalline materials, including titanium, are made of closelypacked atoms, with “regions of regularity” within these closely packedatoms (i.e. where the atoms have a regular structure, such as8-co-ordination and 12-co-ordination, for example) being referred to as“crystal grains”. Metal consists of a vast number of these crystalgrains. The boundaries of these crystals (i.e. “grain boundaries”) arelocations at which atoms have become misaligned (i.e. the regularstructure is discontinuous). Metals having smaller grains and, thus,more grain boundaries, are harder than metals having larger grains,which have fewer grain boundaries and, as a result, are softer and moreflexible.

Heating of a metal, such as titanium, causes the atoms to move into amore regular arrangement, thereby decreasing the overall number ofcrystal grains but increasing the grain size of the remaining grains(i.e. the number of grains per unit volume decreases). The process bywhich the average grain size increases, so-called “grain growth”,rearranges the crystalline structure of the metal and can causedimensional changes (i.e. dimensional deformation) of the metal andcause the metal to become more flexible.

Titanium has an α-phase, which has a close-packed hexagonal crystalstructure, and a β-phase, which has centered-cubic crystal structure andthat is more open and prone to grain growth than the hexagonalstructure. Titanium transitions from α-phase to β-phase, the so-calledβ-transus, when heated to or above a certain temperature, referred to asthe β-transus temperature. The β-transus temperature is affected byimpurities in the titanium (e.g. iron, carbon, hydrogen), but typicallyoccurs at about 880° C. in commercially-pure titanium. Commercially puretitanium, as opposed to titanium alloys having additive such as aluminum(Al), typically has a microstructure of primarily α-phase grains havingan average grain size in the range of 10-40 μm.

The grain growth of a metal, including titanium, is a function of thetime and temperature for which a metal is heated. For example, while theaverage grain size of commercially-pure titanium increases when heatedto temperatures below the β-transus temperature, such grain growthaccelerates rapidly when the titanium is heated to a temperature at orabove the β-transus temperature and the titanium transitions fromα-phase to β-phase. For instance, the average grain size ofcommercially-pure titanium has been shown to increase in from about10-40 μm to about 70 μm when heated at 700° C. for 120 minutes, to about100 μm when heated at 750° C. for 120 minutes, and to about 180 μm whenheated at 800° C. for 120 minutes. However, the average grain size ofcommercially-pure titanium has been shown to increase in from about10-40 μm to about 350 μm when heated at 1000° C. for 120 minutes, and toabout 425 μm when heated at 1100° C. for 120 minutes.

With reference to conventional feedthrough 50 of FIG. 2, attachingferrule 56 to housing 32 by laser welding or brazing (e.g. gold braze)heats housing 32 to a temperature well above the β-transus temperatureof titanium, resulting in rapid grain growth in the titanium of housing32. For example, the average grain size may increase by 300 μm or more.Such grain growth causes dimensional distortions in housing 32 that cancause opening 46 to be outside of specified tolerances and causes thetitanium about the perimeter of opening 46 to become less rigid, each ofwhich can result in a poor or defective seal being formed betweenhousing 32 and feedthrough 50.

FIG. 3 is a schematic diagram illustrating portions of an implantablemedical device 130, including a housing 132 and feedthrough 150according to one embodiment of the present disclosure. As will bedescribed in greater detail below, insulator 152 of feedthrough 150 isattached directly to housing 132 with a bond material 166 usingultrasonic welding to form an ultrasonic joint 180 that is formed at alow-temperature, which is at least at temperatures below the β-transustemperature of the titanium of housing 132.

By attaching feedthrough 150 directly to housing 132 via insulator 152,the need for a ferrule (such as ferrule 56 of FIG. 2) is eliminated,thereby eliminating the cost of manufacturing such a ferrule as well asthe difficulties and shortcomings associated with attaching such aferrule to the insulator (such as insulator 52 of FIG. 2). Additionally,by attaching feedthrough 150 to housing 132 using ultrasonic welding atreduced temperatures relative to conventional welding or brazingtechniques, dimensional distortions of housing 132 due to the hightemperatures and grain growth of titanium are substantially reduced, atleast to levels that maintain dimensions of housing 132 within specifiedtolerances, and the titanium remains in a more rigid state.

While FIG. 3 is a cross-sectional view illustrating portions of housing132, particularly the location where feedthrough 150 attaches to housing132 to seal opening 146, implantable medical device 130 may includeadditional features similar to those described with respect to medicaldevice 30 of FIG. 1. According to one embodiment, housing 132 is formedof titanium and defines a hermetically sealed interior space 134 inwhich device electronics are disposed and protected from fluids of bodyfluid side 138 external to housing 132. According to one embodiment, aheader, similar to header 40 of FIG. 1, for example, may also beprovided to attach to housing 132, and in some instances includes aconnector block, which typically includes one or more sockets forconnecting to one or more sensing and/or stimulating leads.

Similar to that described above with regard to FIG. 2, feedthrough 150establishes electrical connections or pathways from body fluid side 138to the interior space 134 of housing 132 while maintaining the integrityof hermetically sealed interior space 134 via conducting elements 154which pass through insulator 152. According to one embodiment, insulator152 is a glass or ceramic material, such as aluminum oxide (Al₂O₃).According to on embodiment, conducting elements 154 are formed of acermet.

In the context of one embodiment, the terms, “cermet” or“cermet-containing,” refers to composite materials made of ceramicmaterials in a metallic matrix (binding agent). These are characterizedby their particularly high hardness and wear resistance. The “cermets”and/or “cermet-containing” substances are cutting materials that arerelated to hard metals, but contain no tungsten carbide hard metal andare produced by powder metallurgical means. A sintering process forcermets and/or cermet-containing elements proceeds is the same as thatfor homogeneous powders, except that the metal is compacted morestrongly at the same pressuring force as compared to the ceramicmaterial. The cermet-containing bearing element has a higher thermalshock and oxidation resistance than sintered hard metals. In most cases,the ceramic components of the cermet are aluminum oxide (Al₂O₃) andzirconium dioxide (ZrO₂), whereas niobium, molybdenum, titanium, cobalt,zirconium, chromium and platinum are conceivable as metallic components.

According to one embodiment, such as illustrated by FIG. 3, the ceramic(e.g. Al₂O₃) of insulator 152 and the cermet of conducting elements 154are formed in a first process such that an interface between insulator152 and conducting elements 154 are hermetically sealed without the useof a braze or solder. According to one example of such an embodiment,the ceramic of insulator 152 is a multi-layer ceramic sheet into which aplurality of vias is introduced. The cermet of conducting elements 154is then introduced into the vias. In one embodiment, both materials areintroduced in a green state, and the combination is fired together.According to such an embodiment, the joining of insulator 152 withconducting elements 154 forms a hermetic seal without the use of brazeor solder.

According to one embodiment, ultrasonic joint 180 is formed of abiocompatible bond material 166 and a metalized coating 164 betweenfeedthrough 150 and housing 132. In one embodiment, the outside edges ofinsulator 152 are metalized (such as through a sputter coating process,for example) to provide a thin metal coating 164 thereon. In variousembodiments, the insulator is metalized with biocompatible material suchas gold, titanium, niobium, or various combinations thereof. Ultrasonicjoint 180 formed of bond material 166 and metal coating 164 betweenfeedthrough device 150 and metal housing 132 mechanically andhermetically couples feedthrough device 150 and metal housing 132. Inone embodiment, bond material 166 is formed of a biocompatible metal. Invarious embodiments, gold, platinum, palladium, aluminum, niobium andcombinations of these, may be used for bond material 166.

FIG. 4 is a schematic diagram illustrating a system 200 for attachingfeedthrough 150 to metal housing 132 according to one embodiment of thepresent disclosure. In one embodiment, system 200 is an ultrasonicwelding system including transducer 202, coupler 204, sonotrode tip 206and anvil 208. System 200 is configured to ultrasonically weldfeedthrough 150 to metal housing 132 with a “cold welding” process tocreate ultrasonic joint 180, such that materials of feedthrough 150 andmetal housing 132 stay well below the β-transus of those materials asfeedthrough 150 and metal housing 132 are ultrasonically weldedtogether.

In one embodiment, feedthrough 150, and specifically an outer edge offeedthrough 150, is metalized with thin metal coating 164. Feedthrough150 is then placed within opening 146 of metal housing 132. Bondmaterial 166 is placed in the interface between feedthrough 150 andmetal housing 132 on both sides, and specifically between metal coating164 on the outer edge of feedthrough 150 and metal housing 132.

Feedthrough 150 is then placed between anvil 208 on one side andsonotrode 206 on another as illustrated in FIG. 4. Sonotrode 206 andanvil 208 are then forced together such that feedthrough 150 and metalhousing 132 are clamped therebetween, as is bond material 166, whichfills the interface between them. Transducer 202 is then energizedsupplying ultrasonic energy to sonotrode 206 via coupler 204. Energizingsonotrode 206 causes vibration of feedthrough 150 and metal housing 132and frictional forces at the interface between them such that a weldoccurs at bond material 166 thereby joining feedthrough 150 and metalhousing 132, mechanically and hermetically joining them.

In one embodiment, feedthrough 150 is bonded to metal housing 132 withbonding material 166 with ultrasonic welding using system 200.Ultrasonic vibration is used such that the materials are bonded withoutsignificantly raising the temperature of the materials above, or in oneembodiment even near, the β-transus of the materials. As such, the grainsize of the materials does not experience significant growth. In oneexample where metal housing 132 is titanium, the temperature of themetal housing 132 during ultrasonic welding is kept well below thearound 880-890° C. β-transus temperature. In one case, the temperatureduring ultrasonic welding is kept below 750° C., and in another, below400° C. In either case, the microstructure of the titanium remainsprimarily α-phase grains having an average grain size in the range of10-40 μm and does not reach the β-transus, and does not experiencesignificant grain growth such that there are no or minimal dimensionaldistortions of housing 132.

In various embodiments where feedthrough 150 is bonded to metal housing132 with bonding material 166 using ultrasonic welding using system 200such that a relatively low temperature is maintained during formation,metal housing 132 is a metal material with an average grain size in therange of less than 425 μm, less than 300 μm, less than 180 μm and lessthan 70 μm.

In one embodiment, the outside edges of feedthrough 150, which aremetalized with thin metal coating 164 are angled relative to verticaland the inner edges of metal housing 132 are likewise angled to mirrorthe angle of the outside edges of feedthrough 150, as illustrated inFIG. 4. In this way, as sonotrode 206 and anvil 208 are forced togetheron either side of feedthrough 150 and metal housing 132, the anglededges facilitates the application of force to the interface betweenfeedthrough 150 and metal housing 132 and the welding of bond material166 into ultrasonic joint 180. In one embodiment, bond material 166 is avery thin layer, for example, the layer is less than 100 um.

In the embodiment illustrated in FIG. 4, metal housing 132 is slopedinward, such that opening 146 is smaller at interior space 134 side thanat body fluid side 138. Feedthrough 150 is then shaped to complimentthis slope and is wider at body fluid side 138 and narrower at interiorspace side 134. Also, an outer surface 150 a of feedthrough 150 isdisplaced relative to an outer surface 132 a of metal housing 132, suchthat when force is applied to sonotrode 206 toward feedthrough 150 andmetal housing 132, sonotrode 206 will only contact feedthrough 150, butwill not contact housing 132. Correspondingly, an inner surface 150 b offeedthrough 150 is also displaced relative to an inner surface 132 b ofmetal housing 132, such that when force is applied to anvil 208 towardfeedthrough 150 and metal housing 132, anvil 208 will only contacthousing 132, but will not contact feedthrough 150.

In this way, feedthrough 150 is forced against the angled edge ofhousing 132 as sonotrode 206 and anvil 208 are forced together. Thisforce at the interface between feedthrough 150 and housing 132facilitates ultrasonic joint 180 as system 200 is energized. A similarforce can be created at the interface by inverting the slope of theedges of both feedthrough 150 and housing 132 and also inverting therelative displacement of the two, that is, outer surface 150 a offeedthrough 150 is displaced “down” (as depicted in FIG. 4) relative toouter surface 132 a of metal housing 132, such that when force isapplied to sonotrode 206 toward feedthrough 150 and metal housing 132,sonotrode 206 will only contact housing 132, but will not contactfeedthrough 150 and inner surface 150 b of feedthrough 150 is displaced“down” (as depicted in FIG. 4) relative to inner surface 132 b of metalhousing 132, such that when force is applied to anvil 208 towardfeedthrough 150 and metal housing 132, anvil 208 will only contactfeedthrough 150, but will not contact housing 132.

According to one embodiment, feedthrough 150 has a width W₁₅₀ at awidest point between opposing sloped surfaces that is wider than a widthW₁₄₆ of opening 146 in housing 132 (illustrated in FIG. 3), therebycreating an overlap between feedthrough 150 and housing 132. In thisway, when a force is applied on either side of feedthrough 150 andhousing 132 by sonotrode 206 and anvil 208 as described above, the forceis transferred to the interface between feedthrough 150 and housing 132thereby allowing the formation of ultrasonic joint 180. According to oneembodiment, ultrasonic joint 180 has a thickness T₁₈₀. According to oneembodiment, the thickness T₁₈₀ of ultrasonic joint 180 is in a rangefrom 20 to 200 μm.

FIG. 5 is a schematic diagram illustrating a system 300 for attachingfeedthrough 250 to metal housing 232 for an implantable medical device230 according to one embodiment of the present disclosure. In oneembodiment, system 300 is an ultrasonic welding system includingtransducer 302, coupler 304, sonotrode tip 306 and anvil 308. System 300is configured to ultrasonically weld feedthrough 250 to metal housing232 with a “cold welding” process such that materials of feedthrough 250and metal housing 232 stay well below the β-transus of the materials.

In one embodiment, a lower surface of feedthrough 250 is metalized withthin metal coating 264. Feedthrough 250 is then placed within opening246 of metal housing 232. Furthermore, metal housing 232 is providedwith first and second features 232 a and 232 b, which in one embodimentare ledge-like projections onto which feedthrough 250 can be placed.Bond material 266 is placed in the interface between feedthrough 250 andfirst and second features 232 a and 232 b of metal housing 232.

Feedthrough 250 is then placed between anvil 308 on one side andsonotrode 306 on another as illustrated in FIG. 5. Sonotrode 306 andanvil 308 are then forced together such that feedthrough 250 and metalhousing 232 are clamped therebetween, as is bond material 266, whichfills the interface between them. Transducer 302 is then energizedsupplying ultrasonic energy to sonotrode 306 via coupler 304. Energizingsonotrode 306 causes vibration of feedthrough 250 and metal housing 232and frictional forces at the interface between them such that a weldoccurs at bond material 266 thereby forming ultrasonic joint 280 joiningfeedthrough 250 and metal housing 232, mechanically and hermeticallyjoining them.

As above, in one embodiment, feedthrough 250 is bonded to metal housing232 with bonding material 266 using ultrasonic welding using system 300with ultrasonic vibration such that the materials are bonded withoutsignificantly raising the temperature of the materials above, or in oneembodiment even near, the β-transus of the materials. As such, the grainsize of the materials does not experience significant growth asdiscussed above. As above, in various embodiments where feedthrough 250is bonded to metal housing 232 with bonding material 266 usingultrasonic welding using system 300 such that a relatively lowtemperature is maintained during formation, metal housing 232 is a metalmaterial with an average grain size in the range of less than 425 μm,less than 300 μm, less than 180 μm and less than 70 μm.

In one embodiment, first and second features 232 a and 232 b of metalhousing 232 jog down from a profile of housing 232 and define opening246 therebetween. As such, features 232 a/232 b provide a “ledge”against which feedthrough 250 can rest. Bond material 264 is easilyadded between feedthrough 250 and features 232 a/232 b at theirinterface, as illustrated in FIG. 5. In this way, as sonotrode 306 andanvil 308 are forced together on either side of feedthrough 250 andmetal housing 232, the configuration of features 232 a/232 b facilitatesthe application of force to the interface between feedthrough 250 andmetal housing 232 and the welding of bond material 266. In oneembodiment, the bond material is a very thin layer, for example, thelayer is less than 100 um. Other configurations of first and secondfeatures 232 a and 232 b are also possible. Also, features can be addedto feedthrough 250 that are useful for mating with housing 232 and thatwill allow force applied by system 300 to facilitate ultrasonic weldingat the interface.

According to one embodiment, feedthrough 250 has a width W₂₅₀ at itsopposing outer surfaces that is wider than a width W₂₄₆ of opening 246in housing 232, thereby creating an overlap between feedthrough 250 andhousing 232. In this way, when a force is applied on either side offeedthrough 250 and housing 232 by sonotrode 306 and anvil 308 asdescribed above, the force is transferred to the interface betweenfeedthrough 250 and housing 232 thereby allowing the formation ofultrasonic joint 280. According to one embodiment, ultrasonic joint 280has a total width that is defined by the width W₂₅₀ of feedthrough lessthe width W₂₄₆ of opening 246. This total width of ultrasonic joint 280is split on either side of opening 246. In one embodiment, the widthW₂₅₀ of feedthrough is at least twice the width W₂₄₆ of opening 246 suchthat the total width of ultrasonic joint 280 is sufficient to create agood hermetic seal. According to one embodiment, ultrasonic joint 280has a thickness T₂₈₀, which in one embodiment, is in a range from 20 to200 μm.

FIG. 6 illustrates a method 400 of securing a feedthrough, such asfeedthroughs 150 and 250 above, to a housing, such as metal housing 132or 232 above, for an implantable medical device. At 410, a feedthrough150/250 is provided comprising an insulating section and at least oneconductive section extending through the insulating section. In oneexample, the conductive section is a cermet conductor extending throughthe insulator, which is a ceramic material.

At 420, at least the insulator 152/252 of the feedthrough 150/250 ismetalized with a metal coating 164/264. In one example, themetallization is a sputter coating process. At 430, the feedthrough150/250 is placed in an opening of metal housing 132/232. In oneembodiment, feedthrough 150/250 and the opening of metal housing 132/232are configured with features that are symmetrical such that they fittogether along an interface defined by the features. Furthermore, one ormore bonding materials can be placed in the interface between them.

At 440, the combination of the feedthrough 150/250 and the metal housing132/232 are positioned within an ultrasonic welding system and theultrasonic welding system is energized such that sonic energy welds thefeedthrough 150/250 directly to the metal housing 132/232. At 450, thesystem is controlled such that the temperature of the materials of themetal housing and feedthrough are not raised above the β-transustemperature of the materials during the welding.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. An implantable medical device comprising: a metalhousing configured for implantation in a human and comprising abiocompatible metal and defining an opening; a feedthrough deviceconfigured within the opening of the metal housing and comprising aninsulating section and a conducting section, the insulating sectionelectrically isolating the conducting section from the metal housing;and an ultrasonic joint between the feedthrough device and metal housingthat hermetically and mechanically bonds the feedthrough device andmetal housing; characterized in that the biocompatible metal of thehousing comprises a microstructure primarily having α-phase grains. 2.The implantable medical device of claim 1, further characterized in thatthe biocompatible metal of the housing comprises a microstructure havingsubstantially no β-phase grains.
 3. The implantable medical device ofclaim 1, further comprising a biocompatible bonding material between thefeedthrough device and metal housing.
 4. The implantable medical deviceof claim 1, wherein the biocompatible metal of the housing comprisestitanium, niobium or a combination thereof.
 5. The implantable medicaldevice of claim 1, wherein the biocompatible metal of the housing has anaverage grain size less than 425 μm.
 6. The implantable medical deviceof claim 1, wherein the biocompatible metal of the housing has anaverage grain size less than 300 μm.
 7. The implantable medical deviceof claim 1, wherein the biocompatible metal of the housing has anaverage grain size less than 100 μm.
 8. The implantable medical deviceof claim 1, wherein the biocompatible metal of the housing has anaverage grain size in the range of 10-40 μm.
 9. The implantable medicaldevice of claim 1, wherein an interface between the feedthrough andmetal housing is substantially angled relative an exterior surface ofthe metal housing.
 10. The implantable medical device of claim 1,wherein a width on the opening of the housing is smaller than a width ofthe feedthrough device at its widest distance between two opposingsides.
 11. An implantable medical device comprising: a housing having anopening with an opening width; a feedthrough including an insulatorhaving a bottom surface and side surfaces and having an insulator widthbetween opposing side surfaces that is greater than the opening width;and a ultrasonic joint between at least one of the bottom surface, topsurface, and side surfaces of the insulator and the housing whichhermetically seals the insulator to the housing.
 12. The implantablemedical device of claim 11, wherein the insulator width between opposingside surfaces is two times greater than the opening width.
 13. Theimplantable medical device of claim 11, characterized in that thehousing comprises a biocompatible metal comprising a microstructureprimarily having α-phase grains.
 14. The implantable medical device ofclaim 13, characterized in that the biocompatible metal of the housingcomprises a microstructure having substantially no β-phase grains. 15.The implantable medical device of claim 11, wherein the housingcomprises a metal having an average grain size less than 300 μm.
 16. Theimplantable medical device of claim 11, wherein the biocompatible metalof the housing has an average grain size less than 100 μm.
 17. Theimplantable medical device of claim 11, wherein the biocompatible metalof the housing has an average grain size in the range of 10-40 μm.